Density functional theory investigation of the mechanical, electronic and optical properties of Pb-free vacancy-ordered double perovskites K2PdCl6 and K2PdBr6

The current work has investigated the mechanical, electronic and optical properties of Pb-free vacancy-ordered double perovskites K2PdCl6 and K2PdBr6 by using first-principles calculations based on the framework of density functional theory (DFT). The calculated lattice constants of K2PdCl6 and K2PdBr6 are close to the experiments. It is determined by calculating the Goldschmidt’s tolerance factors and elastic constants of K2PdCl6 and K2PdBr6 that they can be stabilized into 3D cubic crystal structures. The calculated Poisson and Pugh’s ratios indicate that K2PdCl6 is a brittle material, while K2PdBr6 exhibits ductile behavior. Both K2PdCl6 and K2PdBr6 are indirect band gap semiconductors, which show suitable band gaps of 2.151 eV and 1.368 eV for optoelectronic devices, respectively. In addition, the optical properties of K2PdCl6 and K2PdBr6 in the photon energy range of 0−6 eV further reveal the application potential of these compounds in single-junction and tandem solar cells as well as other optoelectronic devices.

Effect of impurity carbon and oxygen atoms on the behavior of hydrogen in vanadium in a fusion environment: A first-principles study

We have investigated the effect of impurity X (X = C and O) atoms on the behavior of hydrogen in vanadium, which is an ideal structural material for nuclear fusion reactors, by first-principles calculations. We found that (1) in bulk V, the interaction between an interstitial H atom and an X atom is repulsive, and the interaction with O is much stronger than that with C. (2) The X–vacancy (vac) cluster can act as a center for capturing H in V. The C-vac cluster can trap as many as two H atoms, while the O–vac cluster can capture up to four H atoms. (3) C and O impurities can effectively decrease the trapping energy of a single H atom in a vacancy. The H-trapping energies in the C–vac and O–vac complexes are 0.88 eV and 0.46 eV, respectively, both of which are lower than those in the X-free vacancy. (4) Both H–X and X-metal interactions affect the H solubility in V. The above results provide important information for application of vanadium as a structural material for nuclear fusion tokamaks.

Effect of carbon on behavior of helium in vanadium: A first-principles investigation

By using the first-principles calculations, we studied the effect of carbon (C) on the behaviors of helium (He) in vanadium (V). The results show that C can effectively reduce the solubility of He in bulk V. Compared with defect-free V bulk, the C-vac complex reduces the charge density around it, which makes it act as a trapping center and promotes He nucleation. The maximum number of He atoms trapped by the C-vac complex is five. Furthermore, the interaction between He and the C-vac complex is slightly stronger than that in a C-free vacancy, which indicates that C could increase the trapping ability of vacancy to He atom. Based on the above results, we conclude that C has a certain influence on the dissolution and the trapping behaviors of He in V.